A radiological terrorist attack (e.g., the detonation of an improvised nuclear device) could result in the exposure of thousands of civilians and first responders to lethal or potentially lethal doses of ionizing radiation (IR). Unfortunately, existin countermeasures are generally ineffective if administered after exposure or are effective only within a narrow dose range. In addition, there are logistical problems associated with the treatment of mass casualties using existing approaches. Thus, there is a major effort in the U.S. to develop countermeasures that would be effective if administered after irradiation, involve easy deployment and use protocols, and are non-toxic. We have identified a novel non-pharmacological strategy which is very effective at mitigating the lethal effects of IR in a female mouse model if administered after exposure, and satisfies many of the criteria of an ideal radiation countermeasure. Our approach involves the creation of a small subcutaneous incision (1 cm) in the mouse within a defined period of time post-irradiation. Our preliminary data suggest that subcutaneous wounding several minutes after irradiation greatly protects against lethality. Mitigation of IR effects and the acute radiation syndrome may be mediated by the modulation of specific cytokines or enhanced recovery of hematopoiesis. However, the optimal parameters for creating the wound to derive maximal radioprotection and the mechanism by which wounding protects against radiation lethality have yet to be elucidated. In this exploratory application, we seek to accomplish two main objectives. The first objective will be to determine the optimal parameters for subcutaneous wounding after irradiation (length of the wound, window of time after irradiation during which wounding is protective), and the maximum dose for which protection may be afforded. To establish the validity of the protective wounding strategy as a radiation countermeasure, and its usefulness in the treatment of mass casualties, we shall determine whether protection against lethality is afforded within a window of up to 48 h post-irradiation. To determine applicability, we will test our strategy on mice of both sexes and of various ages, and assess whether all age groups and both sexes are protected similarly from the lethal effects of IR. To accomplish this, the 30-day survival of mice that have received a wound will be compared with that of mice which were not wounded. The second objective will be to identify potential mechanisms by which wounding after irradiation enhances survival. Specifically we shall compare the temporal pattern of modulation of cytokine profiles, and damage to and recovery of blood elements (and precursors) and the gastrointestinal tract, in wounded and control irradiated mice, and correlate these observations with survival. In addition to demonstrating the validity and general applicability of this non- debilitating protective wounding strategy, the experiments proposed should lead to further development of both non-pharmacological and pharmacological radiation countermeasures.